Change radius for proportional editing
You must press PgUpPgDown or use the scroll wheel during a transform action such as Translate (G), Rotate (R), or Scale (S).
During a transform operation, you can see the proportional size visualized as as a circle around the Pivot point and you can see the actual proportional size value displayed in the Header:

In the Redo panel located at the bottom of the Tool Shelf (N in the 3D view) or found by pressing F6, there is a slider to adjust the Proportional size. Note that this only applies immediately after a transform operation.